The use of filters for the removal of suspended particles from fluids is well known and has been extensively described in the literature. In general, these devices use size exclusion to remove contaminants. More particularly, a given filter which can comprise particles, webs, or papers, has pores within a particular size range. Particles larger than the pores are caught by the filter and removed from the fluid. Particles smaller than the pores may pass through the filter.
Unlike filtration, sorption relies on a chemical or physical interaction between the sorbing species and the species to be absorbed (i.e., the contaminant) in order to remove the latter from a fluid. (Accordingly, sorption can be used to remove dissolved as well as suspended species.) Sorption is most often performed in columns packed with porous granules. Leading from the exterior to the interior of these granules are pores containing what may be termed active sites, i.e., reactive groups bound to the granule or present on the surfaces thereof Optimally, the distance from the exterior of the granule to the active site which the contaminant must travel should be as small as possible. One way to do this is to minimize the size of the granule. However, the minimum size of such granules is limited by the following factors: the size of the openings in the screen used to support the granules in the column and the pressure drop developed by fluids passing through the column. Therefore, column-packing granules have a minimum size below which column sorption becomes impractical.
A known device is a crepe paper filter element in a coiled configuration that has been described in U.S. Pat. No. 3,759,391. The crepe paper is folded into a V-shaped configuration and two adhesively attached spacer strips are described.